This invention relates to an injection molding machine such as die-casting machine or plastic molding machine, and more particularly, an injection piston-cylinder mechanism provided with means for controlling injection pressure of the injection molding machine.
Generally, with an injection molding machine such as die-casting machine or plastic molding machine, in a case where a single-acting injection piston-cylinder assembly is used as a device for injecting molten bath into a mold cavity, it is considerably difficult to use any conventional control means to adjust a time of raising a pressure in the cylinder of the injection piston-cylinder assembly at a time of the completion of the injection of the molten bath into the mold cavity due to the single-acting injection piston, i.e. to adjust the rising of the pressure acting on the molten bath, because it is considerably hard to incorporate into the injection molding machine control valves such as pressure control valve and flow control valve having quick response ability and sufficient precision.
Actually, pressure in the piston-cylinder mechanism rises quickly at an injection operation, so that high pressure affects on the surface layer of a die-cast product before the surface layer has been completely solidified thereby to break the solidifying surface of the product, which causes formation of burrs thereon.
There is also known an injecting molding machine which includes a booster piston-cylinder assembly in a case where an injection pressure in addition to that applied by a single-acting injection piston will be required to inject the molten bath into a mold cavity or where it is required to quickly raise the pressure for injecting the molten bath thereinto.
However, in such cases, a surge-pressure over a preset pressure is additionally caused and applied to the mold at a time of compression of the injection, so that the pressure applied to the injected molten bath is over thereby to unwillingly open the mold, which causes the formation of the burrs on the surface of the mold product.